Microsized devices include, for example, micro-accelerometers and micro-gyroscopes for detecting linear and angular accelerations as manufactured by Analog Devices, Inc., chemically sensitive field effect transistors, used to detect the presence of certain molecular vapors such as carbon monoxide or ethanol, pressure sensors for measurement of pressures in automotive systems or micro phonic sensors, such as those employed in cell phones to detect and reproduce audio sounds, and optical sensors for detecting the presence of objects by infra-red radiation. These and other microsized devices are well known to practitioners of micro systems technology (MST). Also well known in that art are the difficulties encountered in inexpensive packaging of such microsized devices, in part because their small sizes require accurate positioning of connections and also because the connections may be of many different types, for example electrical, mechanical, or fluidic (vapor). Because the objects are small, many interconnected devices may be incorporated for systems applications. Additionally, since the devices are small, connections must be made so as not to perturb their functionality, for example by mechanical stress, especially in the face of changes in external environment in which collections of devices are operated, such as temperature or humidity.
Previous means employed for the connection of microdevices have included the use of automated wire bonding apparatus, use of ball grid arrays technology, fabrication of special packages using materials having temperature matched expansion coefficients, and the use of packages encapsulating devices in inert or chemically controlled atmospheres. Although these techniques offer sophisticated solutions, their implementation is not without expense, as is well known, for example, in the case of the packaging of micromirror devices (MMD) as manufactured by Texas Instruments, Inc. More recently, lower cost solutions have become available for mounting and connecting arrays of microsized devices on polymer films, for example those using films on which are patterned conductive lines, which may be deposited by many techniques, including ink jet printing of fluids. Such fluids may be conductive as deposited or may become conductive upon subsequent processing, for example by thermal annealing. These films are typically flexible and therefore are less likely to perturb the functionality of the microsized devices by mechanical stress.
One means of depositing conductive lines, related to the present invention, is by depositing conductive fluids to fill channels made in polymer films, for example channels made by laser ablation of polymer films, hereinafter referred to as ablative films. As is well known in the art of MST, microsized devices may then be placed proximate to the conductive lines; and connections, typically electrical, may be made using a variety of techniques, including wire-bonding, flip chip bonding, electroplating, and deposition of conductive materials, including deposition of conductive fluids by inkjet means, typically to ensure the reliable connection of electric leads to the devices or “die.”
Referring to FIG. 1a, there is shown a cross-section of a prior art ablative film 5. The ablative film 5 includes a substrate 10, typically a flexible polymer such as a polyamide or polycarbonate, and one or more energy-absorbing layers 20 which can be removed, all or in part, by exposure to intense radiation, or in other words, can be ablated, for example by radiation from a near IR laser. Ablative film compositions which can be removed by radiation from a near IR laser are disclosed, for example, by M. Zaki Ali, et al. in US Patent Publication 2005/0227182, which further contemplates using the ablative films, once ablated, as photolithographic masks for subsequent image wise ultraviolet exposure of flexography materials. The ablative films described in US 2005/0227182 may contain additional layers which serve purposes other than of a substrate or of energy absorbing layers, for example release layers used in lamination and surface energy control layers for repelling liquids, so that the ablative films, once ablated, may serve a variety of purposes. Many other material types of polymeric ablative films and laser ablation processes are well known in the art of laser ablation and laser processing for the manufacture of patterns and structures. For example, U.S. Pat. No. 7,115,514 by Richard Stoltz and assigned to Raydiance, Inc., describes a laser ablation process using short pulses at wavelengths shorter than the near IR are described for ablating a wide variety of materials including metals and inorganic materials and for altering their surfaces by ablation.
Referring to FIG. 1b, there is shown a cross-section of another prior art ablative film 5 of a more complex structure. The ablative film 5 includes a substrate 10, and multiple layers 30, some of which are energy absorbing layers. These layers can be removed, all or in part, by exposure to intense radiation. Other layers may provide desired colors or surface properties, such as hydrophobicity, or may comprise release layers to allow separation of the layers, and may be removed (ablated) when nearby underlying or overlying energy absorbing layers absorb radiation.
Referring to FIGS. 2a-2b, there is illustrated in cross-section and top-view, respectively, prior art formation of a channel 40 in an ablative film 5 of FIG. 1a. The ablative film 5 includes the two energy-absorbing layers 20 and the substrate 10 as described above. The base 50 of the channel 40 may be altered by the ablation process, for example its surface may be rendered hydrophilic.
Among the many known uses for ablative films, subsequent to patterning by ablation, are those relying on the geometry and surface properties of the ablated film to confine deposited fluids, such as fluids containing conductive materials such as metallic particulates. These fluids are typically deposited by well-known techniques such as ink-jetting or immersion in fluid baths followed by removal, for example by mechanical wiping blades, of excess fluid not in the ablative channels. Referring to FIG. 2c, there is illustrated in cross-section a prior art process for forming an electrically conductive material 60 in an ablated channel 40 in the ablative film 5. For example, the conductor 60 may be formed by jetting (preferably by inkjet printing means) a liquid containing a metallic precursor into the channel 40 and then annealing the liquid to form the conductor 60. The conductor 60, as commercialized, for example by Dimatix, Inc. and Cabot Corporation.
The deposition of conductors in channels formed in polymeric films has further been employed to connect together microsized devices electrically, for example by positioning microsized devices on the top surface of polymer films having conductors patterned in channels or on the film surface, the positioning means being one of mechanical placement or, alternatively self assembly, as practiced by Alien Technologies, Inc. The microsized devices are positioned in an approximate way near the conductors and then one or more conductive metal strips are deposited which extend from the microsized device(s) to the conductor(s) to establish electrical connections. Methods of self-aligned positioning include alignment by matching geometrical features built into both the microsized devices and the substrate or the use of chemical constituents deposited pattern wise on the substrate which attract matching chemical constituents applied to the microsized devices as referenced in Sharma, et al., US Patent Publication 2006/0134799 and Sharma, et al., US Patent Publication 2006/0057293. For example, optically emitting diodes arrays may be so formed for display applications.
Although such prior art techniques can provide useable arrays of interconnected devices, the process of placement of the microsized devices must be sufficiently accurate to allow for the cost effective provision of connections, for example connections made of conductive metal strips to establish electrical connections. Such accuracy is generally difficult to achieve for self-aligned processes and expensive to achieve by precision pick and place technologies. Moreover, the deposition of conductive strips is expensive; time consuming and problematic as to reliability if the connection is to be robust on flexible substrates. Additionally, such techniques are not generally applicable to connection types other than electrical, for example connections of the fluidic, magnetic, optical, or mechanical types or connections of mixed types.